Field of the Invention
The present invention generally relates to an imaging apparatus, and particularly it relates to an imaging apparatus and a method of tracking of a moving object.
Description of Related Art
In continuous imaging, in which a plurality of imaging operations are successively performed, a subject needs to be kept in focus (tracked) in order to obtain in-focus images even when the subject is moving. That is, the tracking refers to driving of an imaging lens in such a way as to keep a moving subject in focus during a continuous imaging operation (e.g., live-view or movie imaging). A method for driving an imaging lens while estimating an image plane position at a time of each imaging operation in order to track a subject is known. In Japanese Patent Application Laid-Open No. 8-75999, a method is disclosed in which an imaging lens is driven between frames (between exposure control operations) on the basis of past results of focus detection before a result of calculation of the focus detecting is obtained.
In Japanese Patent Application Laid-Open No. 8-75999, however, a subject is assumed to be moving towards a camera and the like, and the imaging lens is not driven for a subject whose image plane speed (image plane moving speed) is equal to or higher than a certain value (fast-moving subject). This is because a moving direction of such a subject is likely to reverse or change instantly, and if the imaging lens is driven in the above-described manner, the imaging lens might go past an appropriate focus position.
If the imaging lens is not driven for a fast-moving subject before the focus detection for a next imaging operation and is driven only in a short period of time from completion of the focus detection to an imaging operation, it becomes difficult for the imaging lens to accurately track a fast moving subject. If the imaging lens does not appropriately track the subject, the subject might be out of focus in the imaging operation. It is therefore desirable to improve the tracking accuracy of the imaging lens, in particular, for tracking a moving subject that unexpectedly reverses or changes its moving direction.